Urban heat islands (UHIs) are isolated regions found in metropolitan settings that have much hotter temperatures than the surrounding rural areas.
The accumulation of heat-absorbing materials in urban environments, changes to the terrain, and human activity are the main causes of UHIs.
They are a byproduct of urbanization and can affect energy use, the environment, and public health in different ways.
Use of Heat Absorbing Materials:
Materials like concrete and asphalt absorb heat during the day and release it slowly, causing elevated nighttime temperatures.
Buildings with dark surfaces reduce albedo, increasing heat absorption.
Inappropriate Construction:
Buildings constructed close to each other limit airflow, creating heat-trapping spaces and causing higher temperatures.
Absence of Greenery:
The lack of plants, trees, and green spaces reduces natural cooling through shade, worsening the heat island effect.
Poor tree density increases exposure to higher temperatures. In some Indian cities, there is only one tree for 50 to 450 people, while the ideal ratio should be seven trees per person.
Dark, dry surfaces in direct sunlight can reach temperatures of up to 88°C, while vegetated surfaces may only reach 18°C.
High Energy Demands:
Metropolitan cities have higher energy demands for transportation, industrial processes, and air conditioning, which release heat into the air.
Air conditioners emit hot air, creating a cascading effect of increased heat.
Transportation systems produce significant heat due to fossil fuel combustion, exceeding the cooling capacity of incoming winds.
Presence of Pollution:
Urban heat islands have poorer air quality due to trapped pollutants.
Warm water from cities harms the quality of nearby streams, affecting local flora and fauna.
Effects of Urban Heat Island
Health Hazards
Increased risk of heat-related illnesses and deaths.
Vulnerable groups, such as the elderly, infants, pregnant women, slum dwellers, and outdoor workers, are at higher risk.
Environmental Hazards
Contributes to global warming by increasing overall temperatures in urban areas and beyond.
Leads to lower air quality due to higher fossil fuel consumption and pollution.
Water bodies become polluted due to increased pollution levels.
Summer nights no longer provide relief from daytime heat.
Temperature differences within urban areas can reach up to six degrees centigrade, influenced by construction materials, building density, road materials, tree cover, and presence of water bodies.
Power Outages & Increase in Energy Cost
Strain on energy sources leads to higher energy costs and power outages during peak demand.
Each 1°C increase in temperature raises energy demand by 0.5% to 5%, depending on local level of air conditioning penetration.
Mitigation srategies:
Urban Planning
Incorporate green spaces, parks, and trees to provide shade and promote natural cooling.
City-specific management plans, like Heat Action Plans, should prioritize green spaces and water bodies to target all heat generators.
Green infrastructure, such as planting trees and vegetation, helps reduce greenhouse gases and increases evaporation and transpiration, keeping regions cool.
Cool Roofs and Pavements
Implement cool roofs and pavements to reflect sunlight and reduce heat absorption in urban areas.
Examples include Ahmedabad's Cool Roofs programme, which offers affordable solutions for reducing the urban heat island effect.
China and Japan are investigating cool pavements, looking at light-colored paints, unique coatings, etc. that reflect sunlight, help reduce surface temperatures, and lessen the effects of heat islands. These innovations are being studied in Delhi and Pune.
Energy-Efficient Buildings
Promote energy-efficient building designs and use cool building materials to reduce heat emissions.
Adhering to environmentally sustainable solutions, like the Green Building Code, makes buildings more eco-friendly.
Install green roofs and walls to reduce surface temperatures and improve air quality.
Transportation Planning
Encourage public transportation, biking, and walking to reduce vehicular heat emissions.
Technological advancements in transportation, like cool pavements, help lower surface temperatures and mitigate heat island effects.
Sustainable Management
Address the urban heat island issue through comprehensive urban design, economic policy, city management, and sustainable living.
Incorporate heat-resilient designs based on building orientation, location, and materials to maximize shade, create green spaces, and promote natural ventilation.
Innovations
Incorporate architectural-led innovations, such as running cold water through pipes in houses, to mitigate heat.
Adapt ancient building designs for modern facilities to maximize natural cooling and ventilation.
By connecting these strategies, urban areas can effectively mitigate the urban heat island effect, improve public health, and enhance the overall quality of life for residents.
